Wednesday, April 30, 2014

The mystery of a bizarre quacking sound heard in the ocean has finally been solved, scientists report.

The noise - nicknamed "the bio-duck" - appears in the winter
and spring in the Southern Ocean. However, its source has baffled
researchers for decades.

Now acoustic recorders have revealed that the sound is in fact the underwater chatter of the Antarctic minke whale.
The findings are published in the Royal Society journal Biology Letters.
Lead researcher Denise Risch, from the US National Oceanic
and Atmospheric Administration (Noaa) Northeast Fisheries Science Center
in Massachusetts, said: "It was hard to find the source of the signal.
"Over the years there have been several suggestions... but
no-one was able to really show this species was producing the sound
until now."

Lars Kindermann and Ilse Van Opzeeland of the Alfred Wegener Institute obtained this sound recording, which -- although it sounds like the quack of a mechanical waterfowl -- is actually a minke whale.

The researchers attached acoustic monitoring tags to the whales to eavesdrop on them

If it quacks like a duck

The strange sound was first detected by submarines about 50
years ago.
Those who heard it were surprised by its quack-like
qualities.

Since then, the repetitive, low frequency noise has been
recorded many times in the waters around the Antarctic and western
Australia.
Suggestions for its source have ranged from fish to ships.

The researchers now say they have "conclusive evidence" that the bio-duck is produced by the Antarctic minke whale.
In 2013, acoustic recorders were attached to two of the marine mammals and recorded the whales making the strange noise.
Dr Risch said: "It was either the animal carrying the tag or a close-by animal of the same species producing the sound."
The researchers do not yet know under what circumstances the minke
whales make their distinctive vocalisations, although the sounds that
were recorded were produced close to the surface and before the mammals
made deep dives to feed.

The team says solving this long-standing mystery will help them to learn more about these little-studied animals.
Dr Risch said: "Identifying their sounds will allow us to use passive acoustic monitoring to study this species.
"That can give us the timing of their migration - the exact
timing of when the animals appear in Antarctic waters and when they
leave again - so we can learn about migratory patterns, about their
relative abundance in different areas and their movement patterns
between the areas."

The team will be analysing data from the PALAOA station, the
Alfred Wegener Institute's (AWI) permanent acoustic recording station in
Antarctica, which has been recording in the Southern Ocean continuously
in the last few years.
This is not the only acoustic puzzle that scientists have recently shed light on
Another baffling low frequency noise - called The Bloop - turned out to be the sound of Antarctica's ice cracking.